Anode plate for x-ray tubes



Dec. 3, 1968 ELSAS 3,414,754

ANODE PLATE FOR X-RAY TUBES Filed Nov. 16, 1956 Y INV ENTOR A'dofi f/aas ATTYS.

United States Patent 3,414,754 ANODE PLATE FOR X-RAY TUBES Adolf Elsas, Zeckern, Germany, assignor to Siemens Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Filed Nov. 16, 1966, Ser. No. 594,816 Claims priority, application ggmany, Nov. 20, 1965,

9 9 Claims. (Cl. 313-60) ABSTRACT OF THE DISCLOSURE An anode for X-ray tubes wherein the electron impact area consists of an alloy of refractory metal comprising an alloy of tungsten-iridium consisting of iridium contents in the range of between 0.05 and 3% The invention is concerned with anode plates for X-ray tubes in which, at least, the electron impact surface consists of an alloy being formed of tungsten and at least one other refractory metal.

It is known that when anode plates of tungsten are used, the electron impact surface is gradually roughened owing to the load to which the tube is subjected while radiation is generated and that the roughening of the impact surface reduces the radiation output. The roughen ng of the impact surface was largely reduced by providing the electron impact surface with rhenium and its alloys which are softer and more ductile than tungsten. However, rhenium is very expensive so that its use in sufficient quantities proves prohibitive for reasons of economy. Consequently rhenium is being used as an alloy with tungsten and with a rhenium content of 1 up to 35% adequate alloys were obtained. Moreover, 5 up to 25% of the tungsten content of these alloys were replaced by refractory metals such as niobium or tantalum for example. Such alloys, however, still prove to be relatively expensive. Hence, it was decided to apply them by layers which form at least the anode plate surface hit by the electrons. Anode plates provided with a layer which contains rhenium still turned out to be rather expensive.

According to the invention a reduction of costs for anode plates in which at least the electron impact surface is formed by an alloy of refractory metals was obtained by using an alloy of tungsten-iridium containing a tungsten content up to 99.95% and an iridium content from 0.05 to 3% approximately. The preferred content of iridium is 0.1 to 1%.

Starting from the known finding that with tungsten alloys containing additives to increase ductibility a portion of up to 25% of the tungsten content can be replaced by one or several other refractory metals and that in accordance with the invention the iridium content shall amount to about 3%, a tungsten content of up to 72% is attained.

By using a tungsten-iridium alloy a metal of greater hardness is produced as compared with tungsten-rhenium alloys. According to the opinion on the effect of the tungsten-rhenium alloy an impairment of the anode plate would develop when iridium is used as alloy ingredient. Moreover, an unfavourable reduction of the usability of the alloy would be brought about because of the lower melting point of iridium an compared with rhenium. However, it is surprising to see that already 0.3% of iridium sufiices to obtain the effect which is achieved by adding 5 to rhenium. For instance, a tube whose anode plate is provided with an electron impact surface made of a tungsten-iridium alloy, iridium accounting for 0.3%, shows after 24,000 loadings a decrease of the radiation output which is also found in tubes whose electron im- 3,414,754 Patented Dec. 3, 1968 pact surface is formed by a rhenium-tungsten alloy, the rhenium content accounting for 10%. A cost reduction is obtained for the anode plates made in accordance with the invention by the possibility of lessening by a factor of 15 to 30 the quantity of iridium required for the improvement in the alloy without experiencing an impairment of the properties. The iridium content can be limited to 3% because this percentage allows the desired improvement to be obtained to such an extent that increasing the iridium content would no longer prove rewarding economically. Apart from this, if the iridium content is increased considerably in excess of 3%, this would lower the melting point and the heat conductivity, factors tending to lessen the tube rating. When the limit of 3% of the iridium content is exceeded slightly, the quality of the alloy is changed also only slightly and therefore this would still fall Within the scope of the invention.

Moreover it proves to be of advantage that because of the smaller quantity of the required iridium content and the resulting cost reduction of the material the whole anode is made of the alloyed material. In this manner the necessity of applying a compound layer is eliminated.

When the iridium alloy covered by the invention is used in a so-called compound anode, a surface layer, usually 0.1 to 2 mm. thick, is applied to a base of tungsten or molybdenum or an alloy of these metals. Here again the share of expansive additives is smaller than with known tubes so that a reduction of cost is ensured.

The accompanying illustration shows an example of a rotary anode tube 1 embodying the inventive idea and representing a sectional view with a cut-away envelope and rotary anode plate. The glass envelope 2 embraces cathode 3 fitted at one envelope end with leads 4 and the rotary anode 5 fitted at the other end. Both envelopes 2 and cathode 3 as well as rotary anode 5, consisting of rotor '6 and anode plate 7, are arranged and supported in a known manner. Plate 7 is provided with carrier 8 made of molybdenum and tungsten alloy which contains 5% tungsten and molybdenum and the unavoidable impurities. Electron impact surfaces 10 and 11, which are differently inclined with respect to plate spindle 9, are formed of a 1 mm. thick layer 12 of tungsten alloy with iridium accounting for 0.3 and molybdenum for 5%. The layer 12 is formed of an alloy, which is an example embodying the inventive alloy of tungsten and iridium with tungsten accounting at least 87%, iridium up to 3% and molybdenum up to 10% approximately. In order to obtain, in accordance with the inventive idea, an improved loadability, it is also possible to provide stationary anodes of X-ray tubes with an impact surface containing iridium.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment .is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changed which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed is:

1. An anode plate for X-ray tubes in which at least the electron impact surface consists of refractory metal alloy, the alloy being formed of tungsten-iridium with tungsten accounting up to 99.95 percent and with iridium accounting from 0.05 up to 3 percent approximately.

2. An anode plate for X-ray tubes according to claim 1 which consists of a tungsten-iridium alloy also outside its electron impact surface.

3. A rotary anode X-ray tube having an anode plate in which at least the electron impact surface is formed of a tungsten-iridium alloy with tungsten accounting up to 99.95 percent and with iridium accounting from 005 up to 3 percent approximately.

4. A rotary anode X-ray tube having an anode plate according to claim 1 which consists of a tungsten-iridium alloy also outside its electron impact surface.

5. An anode plate for X-ray tubes having an anode body with an exposed electron impact surface, and electron beam means for producing an electron beam impinging on said surface and causing emission of X-rays therefrom; said electron impact surface consisting of an alloy of tungsten, iridium, and a refractory metal wherein iridium comprises 0.05 to 3% of the alloy and at least 75% of the remainder consists of tungsten.

6. An anode plate for X-ray tubes having an anode body with an exposed electron impact surface, and electron beam means for producing an electron beam impinging on said surface and causing emission of X-rays therefrom; said electron impact surface consisting of a tungsten-mo]ybdenum-iridium alloy containing up to 10% molybdenum, 0.05 to 3% iridium, and the remainder of tungsten.

7. An X-ray tube having an anode body with an exposed electron impact surface, and electron beam means for producing an electron beam impinging on said surface and causing emission of X-rays therefrom; said electron impact surface consisting of a tungsten-iridium alloy containing up to 99.9% tungsten and from 0.1 to 1% iridium.

'8. An X-ray tube having an anode body with an exposed electron impact surface, and electron beam means for producing an electron beam impinging on said surface and causing emission of X-rays therefrom; said electron impact surface consisting of a tungsten-iridium alloy containing 99.7% tungsten and 0.3% iridium.

9. An X-ray tube having an anode body with an exposed electron impact surface, and electron beam means for producing an electron beam impinging on said surface and causing emission of X-rays therefrom; said electron impact surface consisting of an alloy of iridium and another refractory metal and consisting of 0.05 to 3% iridium and tungsten in an amount of at least 75 of the remainder.

References Cited UNITED STATES PATENTS 3/1917 Wiggin 313-330 X 

